The present invention relates to a cellular structure in which the cells or channels are not parallel to the axis of extrusion or the flow axis. In particular, the invention relates to honeycomb structures having twisted or spiral cells and rotationally displaced cross-sections.
Extruded honeycomb structures are traditionally formed with straight and parallel cells or passages which communicate between opposing inlet and outlet faces of the structure. However, straight and parallel cells are not appropriate for certain applications. In some applications it is desirable to provide a tortuous path for the fluid in order to create pseudoturbulence or enhanced mixing within the channels or passages, or ensure contact of fluid particles with the cell walls. Such non-straight paths lead to more thorough heating and/or cleaning as the case may be, as the fluid will undergo prolonged contact with the heat exchanger, catalyst or filter. For example, in trickle bed reactors, fixed bed reactors, automotive reactors, heat exchangers, NOx abatement reactors and other similar applications such as chemical reactors, it is desirable to have the fluid flow through a distorted (non-straight) path to achieve better contact between the reactants and the cell walls. In the case of a heat exchanger for example, improved contact with the cell walls will result in better heat transfer.
In the past, production of cellular structures having non-parallel channels or cells, for example cross-directional flow structures, has required multiple steps involving basically, a cut and paste approach. However, to the best of our knowledge, there has been no disclosure of an extruded honeycomb structure which, as extruded, comprises non-parallel cells, or of a method of making such structures.
Recently, in co-pending, co-assigned U.S. Ser. No. 08/341,667, now U.S. Pat. No. 5,525,291, a novel method is disclosed for extruding honeycomb structures having cross-directional flow cells by using a movable die in which the lateral or reciprocating movement of the die results in a complex cell alignment.
There continues to be need for non-parallel cell structures and for improved methods for making such structures. Accordingly, it the object of the invention to provide a twisted cell honeycomb structure and method of making same.